1. Field of the Invention
The present invention relates to emulsion processes for making rubber latex, rubber latex made therefrom, and graft copolymers made therefrom, and more particularly relates to emulsion processes for making diene rubber latex, diene rubber latex, and graft copolymer made therefrom.
2. Description of the Related Art
Batch processes for making diene rubber latex are known, see, for example, Fronzon, et al., U.S. Pat. No. 4,070,324, issued Jan. 24, 1978, and Miller, et al., U.S. Pat. No. 3,563,946, issued Feb. 16, 1971, both of which are incorporated herein by reference. Batch processes have generally (a) had undesirable heat generation patterns with heat generation peaking as latex viscosity is peaking thereby creating peak heat removal demand from the liquid phase when liquid phase heat removal is at its most inefficient due to the high liquid viscosity, (b) utilized less than substantially all of the vessel volume due in part to the liquid volume shrinkage during the process, (c) required undesirably long reaction times in order to control heat removal from the exothermic reaction, and (d) required high peak loads on the heat removal equipment. Such processes also undesirably typically provided somewhat broad rubber particle size distributions and provided high levels of very small particles ( less than 500A).
Consequently, there is a need to provide a batch type emulsion diene polymerization process which (a) exhibits peak heat generation during the most efficient heat removal period of the process, (b) utilizes an increased volume of the reactor vessel for the final liquid latex, (c) produces an increased level of diene rubber for a given vessel size, (d) maintains a reduced latex viscosity throughout the process and (e) minimizes the amount of unreacted diene monomer in the vessel. There is also a need for a batch type process that provides narrow particle size distribution for use in making graft copolymers.
The present invention provides a semi-batch process for making diene rubber latex in a pressure vessel. The process involves (a) providing the vessel with an initial liquid batch composition comprising water, emulsifier and diene monomer and optionally inorganic and organic salts, (b) feeding into the vessel a liquid feed composition comprising diene monomer and initiator in which the initiator may be dissolved in water. The rate of feed is such that (a) the level of unreacted diene monomer is minimized, (b) peak heat generation occurs early in the process, (c) the process allows for increase production over straight batch processes for a given vessel size, and (d) the process maintains a reduced latex viscosity throughout the process. A rubber latex and graft copolymer made therefrom is also provided.